Undocumented immigrants and supporters hold a vigil at City Hall in San Francisco for Kathryn Steinle, who was allegedly shot and killed by Juan Francisco López Sánchez.
Photograph: Santiago Mejia/Demotix/Corbis

The San Francisco sheriff’s deputies union this week filed a complaint against its own department, over a March memo that emphasised a “sanctuary policy” prohibiting deputies from passing information on arrested individuals to immigration agencies.

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The complaint came less than three weeks after Kathryn Steinle, 32, was shot and killed by an undocumented migrant who had reportedly been deported from the US five times. Steinle’s death sparked a nationwide political debate on immigration, but police and cities that have so-called “sanctuary” policies have largely stood by such laws.

According to the San Francisco complaint, the sanctuary policy “recklessly compromises the safety of sworn personnel, citizens, and those who merely come to visit the San Francisco area”.

The deputies say the city’s policy enabled the death of Steinle, by ignoring alleged requests from immigration officials for information regarding Juan Francisco López Sánchez, who was charged with second-degree murder earlier this month. López Sánchez has pleaded not guilty, telling local news network KGO the shooting was an accident.

San Francisco’s sheriff, Ross Mirkarimi, said he was abiding by a 2013 city policy that permits only certain offenders to be held for deportation.

US Immigration and Customs Enforcement (ICE) issued a statement, which said: “We’re not asking local law enforcement to do our job … all we’re asking is that they notify us when a serious foreign national criminal offender is being released to the street so we can arrange to take custody.”

Despite calls to reduce funding for cities that have sanctuary laws, which have included an attempt by the House appropriations committee to curtail sanctuary cities in its 2016 budget, ICE will see its funding reduced by more than $50m next year.

Politicians have seized on the controversy over López Sánchez’s release from custody and the San Francisco police policy of not handing over undocumented individuals to immigration agencies.

Presidential hopefuls, led by the Republican frontrunner Donald Trump, have lashed out at San Francisco and the scores of other cities who do not inform immigration agencies of arrested undocumented immigrants. Trump argued that San Francisco’s “sanctuary” policy was to blame for a “totally preventable act”.

Without sanctuary policies, Hing argued, “if every time they are talked to by police they are at risk of being deported, why should they cooperate?”

Under a policy of not questioning individuals over their immigration status, he said, people can come forward to give testimony and evidence.

Detractors of sanctuary policies have homed in on the position that had López Sánchez been deported, Steinle would be alive today. Conservatives have called for federal funding to be curtailed if a municipality maintains a “sanctuary” policy.

“It’s time that someone spoke for the victims of these crimes, and their families, instead of the ones who are pulling the triggers,” he said, at a discussion on immigration hosted by the Center for Immigration Studies at the National Press Club in Washington.

While criticism of sanctuary cities has been vocal since Steinle’s death, they are not new. In 1979, Los Angeles was the first city to follow such policies. LA refused to allow its officers to inquire about anyone’s immigration status. Proponents say such a policy helps build a positive relationship between law enforcement and residents.

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The House minority leader, Nancy Pelosi, who is San Francisco’s representative, said she believed in the sanctuary policy and blamed Congress for its failure to act on immigration reform.

“I support the sanctuary policy,” she said, adding that had immigration reform been passed, it could have been “the answer to many of the questions on the subject”.

Hing argued that the overall benefits of sanctuary policies should be understood before rash moves were made. “It is more of a community policing effort,” he said.